The 4WD is basically an acronym for Four Wheel Drive in a car, in which all four wheels receive torque from the engine simultaneously. It basically comes with SUV's (like Toyota Fortuner), as it helps the vehicle to maintain stability and grip on roads while driving on an uneven off-road surface.
On the other hand in 2wd (two wheel drive) only two wheels of the vehicle receive torque from the engine.
Most of the cars come with basic two wheel drive, in which only front wheels receive the acceleration from the engine.
Hi, Generally, Auto makers doesn't sell engine without a chassis. And if you have a problem in your engine, they don't replace the whole engine assembly. After inspecting the problem, only the parts will be changed, which are causing the problem. You can contact to an authorized Tata service station near by you to get information about the engine overhauling cost. To get details about your nearest Tata service station, please visit the link below-